Scientists at HortResearch in New Zealand have successfully bred honey bees that fight back against varroa by rendering the mite's offspring sterile. Since its arrival in NZ seven years ago, varroa has become the number one enemy of bees and beekeepers across much of the country.

Able to reproduce and spread rapidly, the mite lays its eggs inside the brood cells of a beehive where the mites develop to maturity by feeding on bee larvae. Uncontrolled, varroa will usually destroy a bee colony within a year. It is now controlled mostly through the use of chemical miticides at an annual cost to the NZ industry of more than $1.5 million. While such treatments are generally effective, their use is not sustainable says HortResearch honeybee scientist, Dr Mark Goodwin.

Overseas, varroa has quickly built up resistance to these miticides, resulting in large hive losses. In addition, while perfectly safe if used correctly, beekeepers and growers would prefer not to have these chemicals in our natural environment.

The idea to breed 'resistant' bees came from overseas research which showed that varroa mites emerging from certain hives were unable to reproduce. This is due to a genetic trait in the bees themselves called 'delayed suppression of mite reproduction', or SMRD.

Using bees carefully selected from around NZ, Dr Goodwin's team have been interbreeding bees to increase the levels of SMRD within the population.

"With patience we've been able to breed bees whose hives render up to 80% of varroa sterile. The problem is that the process is expensive and time-consuming. We could never rely on artificial insemination to supply the amount of bees needed to continuously replenish the resistance genetics of NZ's 300,000 commercial beehives."

Instead, Dr Goodwin's team hope that they can establish a self-sustaining population of high-resistance bees by keeping them isolated from non-resistant bees.

"An island was the obvious choice for this experiment and we were lucky that Sir Michael Fay and David Richwhite offered us the opportunity to work on Great Mercury Island, which lies off the coast of the Coromandel Peninsula.

"In fact, they've done a lot more than just allow us access to the island. They've shown a real interest in the project and provided staff, equipment, transport and accommodation for visiting staff as well."

Dr Goodwin's team have now transported 50 high-resistance hives to the island, creating an instant population of 500,000 bees.

"Over the next few months those bees will breed and the population will reach around 2.5 million. We'll be watching with interest to see if isolation allows these hives and their offspring to maintain a high degree of varroa resistance," says Dr Goodwin.

If the experiment is successful the island, and possibly others like it, could become vital breeding centres for large numbers of highly resistant queens. These could then form the basis of a continuous flow of new genetics to the mainland, helping to maintain high levels of resistance in commercial hives.